Prolonged incubation of skeletal muscle increases system A amino acid transport

During the course of experiments involving prolonged incubation of skeletal muscle, we observed large increases in system A amino acid transport activity. System A activity was monitored with the nonmetabolizable amino acid analogue alpha-(methylamino)isobutyrate (MeAIB). When rat epitrochlearis muscles are incubated in Krebs-Henseleit buffer supplemented with 0.1% bovine serum albumin and 8 mM glucose, basal MeAIB transport doubles after 5 h and is elevated approximately sevenfold after 9 h compared with rates measured in muscles incubated for 1 h. Insulin-stimulated transport also doubles after 5 h and increases by fourfold after 9 h. The increases in basal and insulin-stimulated system A transport over time can be prevented by incubating muscles in the presence of cycloheximide. Addition of minimum essential medium essential amino acids (EAA) to the incubation medium blocks the increase in basal and insulin-stimulated MeAIB transport measured after 9 h by 85-90 and 60%, respectively. A single amino acid, glutamine, can account for half of the inhibitory effect of EAA on the time-dependent increase in basal system A transport. Amino acid metabolism is not necessary for inhibition of the rise in basal MeAIB transport. At concentrations normally present in minimum essential medium, nonessential amino acids are less effective (51% inhibition) in preventing the rise in basal transport occurring over 9 h. At three times normal concentrations, however, the ability of nonessential amino acids to prevent the time-dependent increases in basal and insulin-stimulated MeAIB transport is comparable to that of EAA. These changes in MeAIB transport with prolonged incubation are not due to muscle deterioration.(ABSTRACT TRUNCATED AT 250 WORDS)

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Ceramide down‐regulates System A amino acid transport and protein synthesis in rat skeletal muscle cells

The FASEB Journal ◽

10.1096/fj.04-2284fje ◽

2004 ◽

Vol 19 (3) ◽

pp. 1-24 ◽

Cited By ~ 71

Author(s):

Russell Hyde ◽

Eric Hajduch ◽

Darren J. Powell ◽

Peter M. Taylor ◽

Harinder S. Hundal

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Amino Acid ◽

Amino Acid Transport ◽

Muscle Cells ◽

Skeletal Muscle Cells ◽

Acid Transport ◽

Rat Skeletal Muscle ◽

System A

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Effect of Na+ electrochemical potential energy on system A Amino acid transport in rat skeletal muscle during endotoxic shock

Amino Acids ◽

10.1007/978-94-011-2262-7_9 ◽

1990 ◽

pp. 71-80

Author(s):

Michael D. Karlstad ◽

John T. Chesney

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Potential Energy ◽

Amino Acid Transport ◽

Endotoxic Shock ◽

Electrochemical Potential ◽

Acid Transport ◽

Rat Skeletal Muscle ◽

System A

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Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction

Reproduction ◽

10.1530/rep.1.00808 ◽

2006 ◽

Vol 131 (5) ◽

pp. 951-960 ◽

Cited By ~ 40

Author(s):

H N Jones ◽

C J Ashworth ◽

K R Page ◽

H J McArdle

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Cell Line ◽

Transport System ◽

Amino Acid Transport ◽

Essential Amino Acids ◽

Acid Transport ◽

Amino Acid Transport System ◽

Transcellular Transport ◽

System A

Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using α(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P< 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 × essential amino acids), SNAT2 mRNA levels showed further significant (P< 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P= 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adaptin vitroto nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

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Testosterone injection stimulates net protein synthesis but not tissue amino acid transport

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1998.275.5.e864 ◽

1998 ◽

Vol 275 (5) ◽

pp. E864-E871 ◽

Cited By ~ 48

Author(s):

Arny A. Ferrando ◽

Kevin D. Tipton ◽

David Doyle ◽

Stuart M. Phillips ◽

Joaquin Cortiella ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Amino Acid ◽

Amino Acid Transport ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Acid Transport ◽

Skeletal Muscle Protein ◽

Net Protein

Testosterone administration (T) increases lean body mass and muscle protein synthesis. We investigated the effects of short-term T on leg muscle protein kinetics and transport of selected amino acids by use of a model based on arteriovenous sampling and muscle biopsy. Fractional synthesis (FSR) and breakdown (FBR) rates of skeletal muscle protein were also directly calculated. Seven healthy men were studied before and 5 days after intramuscular injection of 200 mg of testosterone enanthate. Protein synthesis increased twofold after injection ( P < 0.05), whereas protein breakdown was unchanged. FSR and FBR calculations were in accordance, because FSR increased twofold ( P < 0.05) without a concomitant change in FBR. Net balance between synthesis and breakdown became more positive with both methodologies ( P< 0.05) and was not different from zero. T injection increased arteriovenous essential and nonessential nitrogen balance across the leg ( P < 0.05) in the fasted state, without increasing amino acid transport. Thus T administration leads to an increased net protein synthesis and reutilization of intracellular amino acids in skeletal muscle.

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Effects of prior exercise on the action of insulin-like growth factor I in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1992.263.2.e340 ◽

1992 ◽

Vol 263 (2) ◽

pp. E340-E344 ◽

Cited By ~ 5

Author(s):

E. J. Henriksen ◽

L. L. Louters ◽

C. S. Stump ◽

C. M. Tipton

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Growth Factor ◽

Glucose Transport ◽

Amino Acid Transport ◽

Acid Transport ◽

Factor I ◽

System A ◽

Prior Exercise ◽

Igf I

Prior exercise increases insulin sensitivity for glucose and system A neutral amino acid transport activities in skeletal muscle. Insulin-like growth factor I (IGF-I) also activates these transport processes in resting muscle. It is not known, however, whether prior exercise increases IGF-I action in muscle. Therefore we determined the effect of a single exhausting bout of swim exercise on IGF-I-stimulated glucose transport activity [assessed by 2-deoxy-D-glucose (2-DG) uptake] and system A activity [assessed by alpha-(methylamino)isobutyric acid (MeAIB) uptake] in the isolated rat epitrochlearis muscle. When measured 3.5 h after exercise, the responses to a submaximal concentration (0.2 nM), but not a maximal concentration (13.3 nM), of insulin for activation of 2-DG uptake and MeAIB uptake were enhanced. In contrast, prior exercise increased markedly both the submaximal (5 nM) and maximal (20 nM) responses to IGF-I for activation of 2-DG uptake, whereas only the submaximal response to IGF-I (3 nM) for MeAIB uptake was enhanced after exercise. We conclude that 1) prior exercise significantly enhances the response to a submaximal concentration of IGF-I for activation of the glucose transport and system A neutral amino acid transport systems in skeletal muscle and 2) the enhanced maximal response for IGF-I action after exercise is restricted to the signaling pathway for activation of the glucose transport system.

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Control by amino acids of the activity of system A-mediated amino acid transport in isolated rat hepatocytes

Biochemical Journal ◽

10.1042/bj2310315 ◽

1985 ◽

Vol 231 (2) ◽

pp. 315-320 ◽

Cited By ~ 8

Author(s):

P Fafournoux ◽

C Rémésy ◽

C Demigné

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Cyclic Amp ◽

Amino Acid Transport ◽

High Protein Diet ◽

Basal Diet ◽

Acid Transport ◽

Additional Energy ◽

Isolated Rat Hepatocytes ◽

System A

The effect of amino acids, in concentrations corresponding to those found in the portal vein of rats given a high-protein diet, was investigated on the activity of system A amino acid transport in hepatocytes from fed rats. Amino acids counteracted the induction of system A by insulin or glucagon. This effect was observed at all concentrations of hormones tested, up to 1 microM. Amino acids did not affect the basal cyclic AMP concentration in hepatocytes, or the large rise in cyclic AMP elicited by glucagon. The reversal of system-A induction was observed at relatively low concentration of amino acids, corresponding to plasma values reported in rats given a basal diet. Amino acids were separately tested: substrates of system A were particularly efficient, but so were glutamine and histidine. Non-metabolizable substrates of system A, such as 2-aminoisobutyrate, were also inhibitory, suggesting that a part of the effect of amino acids is independent of their cellular metabolism. Provision of additional energy substrates such as lactate and oleate did not affect induction of system A or the inhibitory effects of amino acids. Thus amino acids do not act by serving as an energy source and by maintaining the integrity of hepatocytes. Inhibition of mRNA synthesis by actinomycin practically abolished the effect of amino acids on the induction of system A by glucagon. The results suggest that amino acids may promote the synthesis of protein(s) affecting the activity of system A either directly at the carrier unit or at an intermediate stage of its emergence.

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Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00062.2006 ◽

2006 ◽

Vol 291 (5) ◽

pp. E1059-E1066 ◽

Cited By ~ 18

Author(s):

Adriana López ◽

Nimbe Torres ◽

Victor Ortiz ◽

Gabriela Alemán ◽

Rogelio Hernández-Pando ◽

...

Keyword(s):

Gene Expression ◽

Amino Acids ◽

Mammary Gland ◽

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Acid Transport ◽

Amino Acid Transport System ◽

System A ◽

Rat Mammary Gland

Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. β-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.

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